1. Field of the Invention
The present invention relates to laser apparatus and methods. More specifically, it relates to switching systems and methods to provide a plurality of selectable low loss paths to, from, and within laser systems.
2. Description of the Prior Art
Some modern optical systems require the use of a single beam coherent light source, such as a laser beam, capable of rapid, efficient, and reliable switching from one wavelength to another. Typically, selectable wavelength beams have been generated by systems comprising multiple laser sources, whose emission beams are selectively directed to a common output path. Alternatively, a plurality of specific wavelengths can be produced from a single laser source, such as Krypton gas, for example.
A very large wavelength range can be achieved when organic dyes dissolved in solvents are used as the laser sources. Typically, each source is pretuned to a fixed wavelength, and excited (pumped) when that wavelength is desired. For dye laser sources, the pumping source is generally other optical emissions such as a flash lamp or another laser source.
Fortunately, the pump emission requirements for many dye laser source are similar and may be the same source, reducing the pump source requirement to only one laser, which is sequentially switched to pump the desired dye laser source. However, this switching of the pump emission to one of several particular dye laser sources (to produce the specific wavelength desired) has traditionally been the `weak link`, imposing limitations on wavelength switching speed, efficiency, and reliability of the switched wavelength laser systems. In addition, a similar problem occurs in switching the paths of emission of each dye laser source to a common output path, when the laser source emissions are sufficiently close in wavelength, to preclude the use of special wavelength selective mirrors.
A simple mechanical device, such as a moving or rotating mirror arrangement may also be used to direct a single pump source to the desired laser source. However, these systems are difficult to operate at high switching rates and may have reliability problems.
A beam deflector utilizing the Bragg effect is described in U.S. Pat. No. 3,609,009, wherein two Bragg angles are formed symmetrically about the incident source light path in a medium by externally induced acoustic waves. This technique is limited by incomplete and multiple mode diffraction, resulting in a loss in transmission, variable diffraction angles, and delays due to the propagation of acoustic waves in the optical media.
Another apparatus is shown in U.S. Pat. No. 3,755,676 wherein gratings forming filters of specific spatial frequency are imposed in the path of spatial frequency multiplexed coherent emission to select out a specific signal. Path selection is accomplished by altering the spatial repetition rates of the gratings or moving the spatial dimensions of the filters. Both of these techniques are relatively slow and complex.
Light beam gating by a Frustrated Total Internal Reflector (FTIR) device has been taught in U.S. Pat. No. 2,997,922. The approach to beam gating is to physically move the media objects toward or apart from each other by mechanical or electromechanical means. The majority of the prior art required considerable energy to operate an FTIR switch between 100% reflectivity and 100% transmission. Similarly, in U.S. Pat. No. 3,711,791, a frustrated total internal reflection (FTIR) switch is used as a Q switch, with incident laser emission either transmitted through a single output path, or reflected back to the laser source.